package DailyPractice.Day6;

import java.util.Scanner;

/**
 * @author lumin
 * @date 2022/04/23 10:53
 **/
public class Num1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int m = sc.nextInt();
        int n = sc.nextInt();
        int[][] arr = new int[m][n];
        int num = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if(arr[i][j] == 0){
                    num++;
                    if(i + 2 < m){
                        arr[i + 2][j] = 1;
                    }
                    if(j + 2 < n){
                        arr[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(num);
    }
}